Scientists have managed to keep a pig heart transplanted into a baboon beating for almost three years, setting a new record and pushing forward the field of cross-species transplantation. The study, from the National Institute of Health, is the result of around 10 years of research into whether or not organs from one species could be transplanted into another.
The study on a handful of primates has blown the previous record of keeping a baboon alive, which was 179 days, out of the water. The median length of time they kept the primates alive for was 298 days, with one baboon managing to survive for an incredible 945.
The transplanted pig hearts didn’t actually replace the baboons' own original organ, but was instead connected to the circulatory system, and then stored in the abdomen, with the original heart stilll operational. This allowed the researchers to study the baboon immune response and potential rejection of the genetically engineered pig heart without having to conduct more difficult heart surgery, while at the same time meaning that the recipient baboon wouldn’t necessarily die from the procedure.
While it is hoped that this could lead us further down the path to conducting the same experiment in humans, this is unlikely to happen for a long time. The experiment didn’t allow the researchers to take the baboons off drugs entirely, which would mean any person with a transplanted heart would also need to be on immunosuppressant drugs their entire lives, which is far from ideal.
The notion for transplanting one species organ into another, known as xenotransplantations, is an old one, but it has been notoriously difficult to achieve. This is because the recipient body of the heart is triggered into producing a powerful immune reaction, which eventually rejects the organ. One of the main causes for this is a protein found on the inside of the pig’s blood vessels, known as alpha 1-3 galactosyltransferase (gal), which causes the recipient's body to mount an immune response and clot the blood.
Genetic engineering has been able to produce pigs that lack the expression of gal on the blood vessels, preventing the blood clotting when transplanted, but this still doesn’t stop the need to dose up the recipient with heavy immune suppressors. These drugs are risky because they are non-specific and suppress the entire immune system, making the patient with the new organ far more likely to succumb to other infections and diseases. The researchers of the new study have instead used more targeted drugs, used in conjunction with heparin, which thins the blood.
“It is very significant because it brings us one step closer to using these organs in humans,” Muhammad Mohiuddin, co-author of the study published in Nature Communications, told AFP. “Xenotransplants – organ transplants between different species – could potentially save thousands of lives each year that are lost due to a shortage of human organs for transplantation.”